\[\sin{110{^\circ}} - \sin{50{^\circ}} =\]
\[= 2\sin\frac{60{^\circ}}{2} \cdot \cos\frac{160{^\circ}}{2} =\]
\[= 2\sin{30{^\circ}} \cdot \cos{80{^\circ}} =\]
\[= 2 \cdot \frac{1}{2} \cdot \cos{80{^\circ}} = \cos{80{^\circ}}\]